My guess is it's the master cylinder leaking into the brake booster.

Try starting the engine, put pressure on the brake pedal and if it slowly sinks to the floor it is either air in the system or more likely the master cylinder is toast.

When you carried out the brake fluid flush through did you use a diag tool to power bleed the braking system including the ABS modulator? .......... if not you may have air in the hydraulic brake system.

Yes I used the Hawkeye to bleed, including the modulator and pedal does not sink

I thought the brakes just plain suck in the Disco. Even the guys at GBR say mine are fine and I think they are pathetic.

Sure sounds like your brake booster. not a tough fix. Don't forget to reset the brake light switch. The major piece of advice I would give is do not buy a reman brake booster. I bought a reman, damn near caused me a major accident. Spend the $500 and buy an OEM one.

I bought a used brake booster five years ago and it’s been just fine. They are generally low failure rate items. I can’t speak to the problem matt3502 had with the reman unit he bought but I wouldn’t be scared of a used one.

mln 01 There is a big difference between a used brake booster and a remanufactured one. With a used one, you accept the possibility that it is not operating to 100%. With a reman, you expect it to be operating very close to 100% as it has been rebuilt to OEM specs. When the reman fails less than 30 days from install the first time you really need the brakes, you know a reman is a total POS. If you value your own life, and the lives of the passengers or any other family member who drives the car, you rethink the concept of used or remanned critical components really quickly.